The present invention relates to a method for controlling the titre of the air-fuel mixture in an internal combustion engine, in particular an internal combustion engine for driving vehicles.
The regulations relating to road vehicles are requiring an increasingly thorough reduction of the pollutant emissions emitted by internal combustion engines. These pollutant emissions can be reduced substantially in two ways: by optimising the combustion process in the cylinders of the engine or by treating the exhaust gases before they are emitted into the atmosphere (typically using exhausts of a catalytic type). In order to optimise the combustion process in the cylinders it is necessary to maintain the titre of the air-fuel mixture as close as possible to the stoichiometric value in each cylinder.
The internal combustion engines that are currently in use are provided with a plurality of cylinders (generally four), each of which has a respective exhaust duct communicating with a common exhaust manifold disposed upstream of an exhaust provided with a device for reducing pollutant agents. In order to contain costs, only the overall stoichiometric ratio of all the cylinders is measured by means of a linear oxygen sensor disposed in the common exhaust manifold.
By means of appropriate reconstruction methods and starting from the measurements of the overall stoichiometric ratio, the stoichiometric ratios of the individual cylinders are estimated and these stoichiometric ratios are used to control the intake of fuel into the individual cylinders, in order to cause each individual cylinder to work as close as possible to the stoichiometric value.
These known reconstruction methods for estimating the stoichiometric ratios of the individual cylinders from the measurements of the overall stoichiometric ratio are, however, relatively imprecise and very complex.
The object of the present invention is to provide a method for controlling the titre of the air-fuel mixture in an internal combustion engine, which is free from the above-described drawbacks and which is, moreover, simple and economic to implement.
In accordance with the present invention, a method for controlling the titre of the air-fuel mixture in an internal combustion engine according to claim 1 is provided.